Ivan S. Dobrovolsky. HARD ENDINGS INSTEAD OF SOFT ENDINGS IN NEW CHURCH SLAVONIC AND OLD CHURCH SLAVONIC GREEKISMS
Trudy IRY RAS. 2023. № 1 (35), Pages. 91 - 101

Andrey A. Zaliznyak. From Russian morphonology: закалять and закаливать
Trudy IRY RAS. 2016. № 3 (9), Pages. 417 - 432